My rear defroster on my 02 Sonata is not working. There is a wire plug under
my front drivers seat that is not plugged into anything. Could this be the
answer? If not, what is that plug for? I can't find anywhere it could go,
unless I just did not see it. Thanks in advance!

Does the on/off lamp on your defogger switch illuminate? (Check with the
car running. It won't turn on unless the car is running.) If not, start
by checking your fuses. If so, turn it on and go to the rear glass and
check to see if you have 12V between the two terminals. If you get the
12V, you're looking at a grid problem. If you don't, you're looking at a
problem elsewhere. You'll probably want to get a schematic if that's the
case.

Most frequently, one of the wires is disconnected or the tab came off the
window.